Kidney stone formers often ask us whether their soda drinking caused their kidney stones. Many have already taken the initiative to cut out all their soda, thinking it will help prevent future stones. So, what’s the real deal with soda and kidney stones?
The belief that soda drinking is associated with increased kidney stone formation stems from a study of 1,009 males randomized to either refraining from or continuing soft drinks over three years by Shushter and colleagues. In their study, those who refrained were 6.4% less likely to form another stone than those who continued their soda intake. Additionally, they observed that those who refrained from sodas acidified by phosphoric acid as opposed to sodas acidified with citric acid had a more pronounced 15% lower likelihood of forming another stone (Shuster et al, J Clin Epidemiol, 1992). Phosphoric acid is most commonly used in colas (such as Coca Cola) while citric acid is most commonly used in fruit flavored sodas (such as Sprite). Based on this study, avoidance of cola drinks was recommended by some physicians as a way to avoid stones.
Other research has however questioned these early findings. In a study of 45,289 men, intake of 21 different types of beverages and the development of stones was determined over six years. In contrast to the prior study, the authors found that cola intake did not increase stone risk when all factors were considered. They concluded that if a person’s diet was otherwise kept the same, the addition of cola would not increase the risk of stones (Curhan et al, Am Journal Epid, 1996).
Overall, the risk of forming stones from soda drinking appears to be questionable. If true, this risk applies to only phosphoric acid containing sodas, found mostly in dark colored sodas. Kidney stoners who want to play it safe can elect to avoid colas and choose non-cola sodas or other non-soda beverages instead. Cola-loving kidney stone formers might choose colas that don’t use phosphoric acid. (You can easily check whether this is in your beverage by reading the ingredients list on the side of the bottle or can). Some cola brands we’ve found that don’t use phosphoric acid include Pepsi Natural and Red Bull Cola*.
In the end, we feel that rather than focusing on the type of fluid they drink, most kidney stone formers are best served by focusing on overall volume-it’s not what you drink but rather how much you’re drinking. That said, given the link between soda drinking and obesity, we feel that drinking water is always a better alternative that has no calories and is cheap if you use the filtered or tap variety.
*We do not endorse (or criticize) any specific soda brands and only use brand names in this article as examples.